The field of the invention is in fluid flow measuring apparatus and more particularly in apparatus for sensing both magnitude and direction of relatively low speed airflows.
The importance of obtaining continuous data which describes the complete velocity vector for flow of air relative to a body traveling through an air mass is well recognized. For instance, this data is necessary to evaluate the aerodynamic performance of parachute systems, balloons, wind sails, kites, and similar airborne devices. This information can be utilized to evaluate the aerodynamic performance of the body independent of the motion of the air mass relative to the earth, e.g., winds and motions of air due to thermal gradients. The testing of low rate of descent final recovery systems and systems incorporating gliding capacility has, prior to this invention, been seriously handicapped by the absence of apparatus for measuring the relative airspeed of descending decelerator systems. Serious analytical error has occured in the past when rates of descent and glide performance are primarily based on the velocity of the test system relative to the earth. In many instances the movements of air masses are larger than the change in system performance erroneously indicated as brought about by an experimental design modification.
Typical examples of the prior art are exemplified by the following patents. U.S. Pat. No. 3,094,869 to patentee G. Wehmann, U.S. Pat. No. 3,304,778 to patentee M. W. Stuart, and U.S. Pat. No. 3,713,336 to patentees Bernstein and Miller.